Work vehicle and power take-off apparatus for the same

ABSTRACT

A work vehicle is provided with a support member that supports an output shaft of a wheel differential mechanism between a differential case and a planetary reduction mechanism. The support member is configured to engage the output shaft relatively immovably in a direction along the axis of the output shaft.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a work vehicle and a power take-offapparatus for the work vehicle.

2. Description of the Related Art (1) First Related Art

There are work vehicles provided with a wheel differential mechanism, anaxle that is located on a vehicle body lateral outer side of the wheeldifferential mechanism, a planetary reduction mechanism that is providedspanning the axle and an output shaft of the wheel differentialmechanism and that downshifts the power of the output shaft andtransmits resultant power to the axle, and a brake that has a frictionplate latched to a region of the output axle between the planetaryreduction mechanism and a differential case of the wheel differentialmechanism and that applies friction braking force to the axle via theoutput shaft.

A tractor shown in JP H10-203185A is an example of this type of workvehicle. This tractor is provided with a rear wheel differentialmechanism serving as the wheel differential mechanism, and with ahandbrake serving as the brake.

In the above-mentioned work vehicle, generally, and the output shaft anda side gear of the wheel differential mechanism are coupled together inan interlocked manner by spline engagement, and the output shaft and arotational member of the planetary reduction mechanism, such as a sungear, are coupled together in an interlocked manner by splineengagement, and thus if the output shaft shifts in a direction along theaxis of the output shaft relative to the wheel differential mechanismand to the planetary reduction mechanism as sometimes happens due tofactors such as operating force acting on the friction plate when thebrake is applied, the brake drags due to the friction plate moving withthe output shaft, resulting in power loss in the drive of the runningwheels. In view of this, a work vehicle that is improved in this respectis desired.

(2) Second Related Art

There are power take-off apparatuses for work vehicles that are capableof shifting the power of an input shaft to power having four differentrotation speeds and taking off resultant power with a power take-offshaft.

For example, an apparatus illustrated in JP S58-043624B (or U.S. Pat.No. 4,292,855A corresponding thereto) is provided with a transmissionshaft serving as the input shaft and a holder serving as the outputshaft that is coupled in an interlocked manner to a power take-off shaft(PTO shaft). Four gears fixed to the transmission shaft, four idlergears freely fitted to the holder in a state of individually meshingwith the four gears, and a link pin that alternatively interlocks thefour idler gears with the holder. That is, the power of the transmissionshaft is transmitted to the holder after being shifted to power havingfour different rotation speeds by four gear trains, and transmitted tothe power take-off shaft from the holder.

In the case of the conventional configuration, four gear trains in whichthe gears are aligned in the direction along the axis of the outputshaft is provided, thus increasing the size of a gear shift mechanism inthe axial direction of the output shaft. In view of this, a powertake-off apparatus that is improved in this respect is desired.

(3) Third Related Art

With work vehicles, even if the engine that is installed differs and therotation speed of engine power that is input to the power take-offapparatus changes, a set rotation speed may need to be maintainedinstead of changing the rotation speed of the power take-off shaft foreach of the four speed levels, due to circumstances specific to theapparatus to be driven. In this case, with a conventional power take-offapparatus, it is necessary to change the speed/transmission ratio of thefour gear trains, thus requiring the provision of a large number ofgears with different outer diameters. This also applies in the case ofchanging the rotation speed of the power take-off shaft for each of thefour speed levels, although the rotation speed of engine power that isinput does not change.

An apparatus having the configuration shown in FIG. 11 will now beconsidered, as a power take-off apparatus that enables the rotationspeed of the power take-off shaft to be shifted through four steps.

That is, a first input shaft gear 151 and a second input shaft gear 152are relatively rotatably supported by an input shaft 150, and a firstoutput shaft gear 154 and a second output shaft gear 155 are relativelyrotatably supported by an output shaft 153. A first relay transmissiongear 156 and a second relay transmission gear 157 are provided to thefirst input shaft gear 151, between the input shaft 150 and the outputshaft 153. When the first input shaft gear 151 is coupled in aninterlocked manner to the input shaft 150 by an input shaft sleeve 158and the first output shaft gear 154 is coupled in an interlocked mannerto the output shaft 153 by an output shaft sleeve 159, the power of theinput shaft 150 is transmitted to the output shaft 153 via the inputshaft sleeve 158, the first input shaft gear 151, the first relaytransmission gear 156, the second relay transmission gear 157, the firstoutput shaft gear 154 and the output shaft sleeve 159, and transmittedto the power take-off shaft 160 from the output shaft 153. When thefirst input shaft gear 151 is coupled in an interlocked manner to theinput shaft 150 by the input shaft sleeve 158 and the second outputshaft gear 155 is coupled in an interlocked manner to the output shaft153 by the output shaft sleeve 159, the power of the input shaft 150 istransmitted to the output shaft 153 via the input shaft sleeve 158, thefirst input shaft gear 151, the first relay transmission gear 156, thesecond relay transmission gear 157, the second output shaft gear 155 andthe output shaft sleeve 159, and transmitted to the power take-off shaft160 from the output shaft 153. When the second input shaft gear 152 iscoupled in an interlocked manner to the input shaft 150 by the inputshaft sleeve 158 and the first output shaft gear 154 is coupled in aninterlocked manner to the output shaft 153 by the output shaft sleeve159, the power of the input shaft 150 is transmitted to the output shaft153 via the input shaft sleeve 158, the second input shaft gear 152, thefirst relay transmission gear 156, the second relay transmission gear157, the first output shaft gear 154 and the output shaft sleeve 159,and transmitted to the power take-off shaft 160 from the output shaft153. When the second input shaft gear 152 is coupled in an interlockedmanner to the input shaft 150 by the input shaft sleeve 158 and thesecond output shaft gear 155 is coupled in an interlocked manner to theoutput shaft 153 by the output shaft sleeve 159, the power of the inputshaft 150 is transmitted to the output shaft 153 via the input shaftsleeve 158, the second input shaft gear 152, the first relaytransmission gear 156, the second relay transmission gear 157, thesecond output shaft gear 155 and the output shaft sleeve 159, andtransmitted to the power take-off shaft 160 from the output shaft 153.

With this power take-off apparatus, the first relay transmission gear156 has a first gear part that engages the first input shaft gear 151,and a second gear part that engages the second input shaft gear 152, andthe second relay transmission gear 157 has a first gear part thatengages the second gear part of the first relay transmission gear 156and engages the second output shaft gear 155, and a second gear partthat engages the first output shaft gear 154. Even with this powertake-off apparatus, it is necessary to adjust the outer diameter of allthe gears, in order to adjust the rotation speed of the power take-offshaft for each of the four speed levels. In view of this, a powertake-off apparatus that can cost effectively adjust the rotation speedof the power take-off shaft for each of the four speed levels isdesired.

SUMMARY OF THE INVENTION

(1) To address the First Related Art, a work vehicle as below isproposed.

A work vehicle comprising:

a wheel differential mechanism having an output shaft and a differentialcase;

an axle located on a vehicle body lateral outer side of the wheeldifferential mechanism and interlocked with the output shaft;

a planetary reduction mechanism provided between the output shaft andthe axle, and configured to downshift power of the output shaft andtransmit resultant power to the axle;

a brake configured to apply friction braking power to the axle via theoutput shaft, the brake having a friction plate latched to a region ofthe output shaft between the differential case and the planetaryreduction mechanism; and

a support member supporting the output shaft between the differentialcase and the planetary reduction mechanism, the support member beingconfigured to engage the output shaft relative immovably in a directionalong an axis of the output shaft.

According to this configuration, even if an operating force that shiftsthe output shaft occurs, the output shaft is securely supported by asupport member against the operating force such that there is noslippage, thus enabling brake drag to be prevented. Also, in the case ofemploying a configuration that prevents shifting of the output shaft byproviding the output shaft with an abutting part that is received andsupported by abutting an end portion of the axle, friction caused byrotation of the axle and the output shaft between the end portion of theaxle and the abutting part occurs, but brake drag can be prevented whileavoiding the occurrence of this friction.

In one preferred embodiment, the support member supports a region of theoutput shaft between the friction plate and the planetary reductionmechanism.

According to this configuration, the region of the output shaft near theplanetary reduction mechanism side is supported by the support member,thus enabling the output shaft to be supported by the support membersuch that power transmission to the planetary reduction mechanism fromthe output shaft is performed in a state where there is no center runoutof the output shaft.

In one preferred embodiment, the support member is a bearing that fitsonto the output shaft.

According to this configuration, the output shaft is supported so as tonot shift while allowing smooth rotation of the output shaft, thusenabling power loss in the wheel drive to be more reliably prevented.

In one preferred embodiment, the brake is configured such that pressureis applied to the friction plate in a direction along the axis of theoutput shaft and the friction plate is pressed against a friction platereceiving part, and the bearing is supported by the friction platereceiving part.

According to this configuration, a friction plate receiving part isutilized for the support member of the bearing, thus enabling thesupport structure of the bearing to be realized with a simple structure.

(2) To address the Second Related Art, a power take-off apparatus for awork vehicle as below is proposed.

A power take-off apparatus for a work vehicle, comprising:

an input shaft;

an output shaft to which power of the input shaft is transmitted;

a power take-off shaft coupled in an interlocked manner to the outputshaft, and configured to take off the power of the output shaft andoutput resultant power to an apparatus to be driven; and

a gear shift mechanism configured to shift the power of the input shaftto power having four different rotation speeds and transmit resultantpower to the output shaft,

wherein the gear shift mechanism includes:

a first gear train having a first input shaft gear relatively rotatablysupported by the input shaft and a first output shaft gear relativelyrotatably supported by the output shaft, and configured to transmit thepower of the input shaft to the output shaft at a firstspeed/transmission ratio, in response to the first input shaft gearbeing coupled in an interlocked manner to the input shaft and the firstoutput shaft gear being coupled in an interlocked manner to the outputshaft;

a second gear train having a second input shaft gear relativelyrotatably supported by the input shaft and a second output shaft gearrelatively rotatably supported by the output shaft, and configured totransmit the power of the input shaft to the output shaft at a secondspeed/transmission ratio different from the first speed/transmissionratio, in response to the second input shaft gear being coupled in aninterlocked manner to the input shaft and the second output shaft gearbeing coupled in an interlocked manner to the output shaft; and

a relay transmission shaft coupled in an interlocked manner to the firstoutput shaft gear via a first relay transmission gear mechanism having afirst relay speed/transmission ratio, and coupled in an interlockedmanner to the second output shaft gear via a second relay transmissiongear mechanism having a second relay speed/transmission ratio differentfrom the first relay speed/transmission ratio, and

wherein the power take-off apparatus further comprises:

a first operation part configured to alternatively couple the firstinput shaft gear and the second input shaft gear to the input shaft inan interlocked manner; and

a second operation part configured to alternatively couple the firstoutput shaft gear and the second output shaft gear to the output shaftin an interlocked manner.

According to this configuration, when the first output shaft gear iscoupled in an interlocked manner to the input shaft in response tooperation by the first operation part and the first output shaft gear iscoupled in an interlocked manner to the output shaft in response tooperation by the second operation part, the power of the input shaft istransmitted to the output shaft via the first gear train, andtransmitted to the power take-off shaft from the output shaft. When thefirst output shaft gear is coupled in an interlocked manner to the inputshaft in response to operation by the first operation part and thesecond output shaft gear is coupled in an interlocked manner to theoutput shaft in response to operation by the second operation part, thepower of the input shaft is transmitted to the output shaft via thefirst gear train, the first relay transmission gear mechanism, the firstrelay transmission shaft, the second relay transmission gear mechanismand the second output shaft gear, and transmitted to the power take-offshaft from the output shaft. When the second output shaft gear iscoupled in an interlocked manner to the input shaft in response tooperation by the first operation part and the second output shaft gearis coupled in an interlocked manner to the output shaft in response tooperation by the second operation part, the power of the input shaft istransmitted to the output shaft via the second gear train, andtransmitted to the power take-off shaft from the output shaft. When thesecond output shaft gear is coupled in an interlocked manner to theinput shaft in response to operation by the first operation part and thefirst output shaft gear is coupled in an interlocked manner to theoutput shaft in response to operation by the second operation part, thepower of the input shaft is transmitted to the output shaft via thesecond gear train, the second relay transmission gear mechanism, thefirst relay transmission shaft, the first relay transmission gearmechanism and the first output shaft gear, thus enabling the power ofthe input shaft to be shifted to power having four different rotationspeeds and taken off by the power take-off shaft.

The gears of the first gear train and the gears of the first relaytransmission gear mechanism can be provided in a state of being alignedin a straight line that passes through the axis of the input shaft andthe axis of the output shaft, and the gears of the second gear train andthe gears of the second relay transmission gear mechanism can beprovided in a state of being aligned in a straight line that passesthrough the axis of the input shaft and the axis of the output shaft.That is, the number of gear trains aligned in the direction along theaxis of the output shaft can be can kept to two, thus enabling the sizeof the gear shift mechanism in the direction along the axis of theoutput shaft to be reduced over the conventional configuration.

In one preferred embodiment, the input shaft, the output shaft and therelay transmission shaft, when viewed in the vehicle body longitudinaldirection, are positioned on a straight line in the vehicle bodyvertical direction. According to this configuration, the input shaft,the output shaft and the relay transmission shaft overlap in a vehiclebody plan view, thus enabling the size of the gear shift mechanism in adirection intersecting the axis of the input shaft to be reduced.

In one preferred embodiment, the first gear train has only the firstinput shaft gear and the first output shaft gear in an engaged state,and the second gear train has only the second input shaft gear and thesecond output shaft gear in an engaged state. According to thisconfiguration, the structure of the first gear train and the second geartrain can be realized with a simple structure that is only provided withtwo shafts, namely, the input shaft and the output shaft.

In one preferred embodiment, the first relay transmission gear mechanismis a first relay transmission gear that is relatively non-rotatablysupported by the relay transmission shaft in a state of engaging thefirst output shaft gear, and the second relay transmission gearmechanism is a second relay transmission gear that is supportedrelatively non-rotatably by the relay transmission shaft in a state ofengaging the second output shaft gear. According to this configuration,the structure of the first relay transmission gear mechanism is realizedwith a simple structure only provided with the first relay transmissiongear, and the structure of the second relay transmission gear mechanismis realized with a simple structure only provided with the second relaytransmission gear.

In one preferred embodiment, the first output shaft gear and the secondoutput shaft gear are supported by the output shaft via a taper rollerbearing.

According to this configuration, in the case of a speed level at whichthe first input shaft gear is coupled in an interlocked manner to theinput shaft and the second output shaft gear is coupled in aninterlocked manner to the output shaft, the first output shaft gear issupported by the output shaft to which the drive load of the powertake-off shaft is applied while being relatively rotatable with respectto the output shaft, and because the first output shaft gear issupported via the taper roller bearing, the first output shaft gearrotates smoothly and power is transmitted smoothly. In the case of aspeed level at which the second input shaft gear is coupled in aninterlocked manner to the input shaft and the first output shaft gear iscoupled in an interlocked manner to the output shaft, the second outputshaft gear is supported by the output shaft to which the drive load ofthe power take-off shaft is applied while being relatively rotatablewith respect to the output shaft, and because the second output shaftgear is supported via the taper roller bearing, the second output shaftgear rotates smoothly and power is transmitted smoothly.

(3) To address the Third Related Art, a power take-off apparatus for awork vehicle as below is proposed.

A power take-off apparatus for a work vehicle, comprising:

an input shaft;

an output shaft to which power of the input shaft is transmitted;

a power take-off shaft coupled in an interlocked manner to the outputshaft, and configured to take off the power of the output shaft andoutput resultant power to an apparatus to be driven;

a gear shift mechanism configured to shift the power of the input shaftto power having four different rotation speeds and transmit resultantpower to the output shaft,

wherein the gear shift mechanism includes:

a first input shaft gear and a second input shaft gear having differentdiameters and relatively rotatably supported by the input shaft in astate of being alternatively coupled in an interlocked manner to theinput shaft;

a first output shaft gear and a second output shaft gear havingdifferent diameters and relatively rotatably supported by the outputshaft in a state of being alternatively coupled in an interlocked mannerto the output shaft;

a first relay transmission gear having a first gear part that engagesthe first input shaft gear and a second gear part that engages thesecond input shaft gear;

a second relay transmission gear having a first gear part that engagesthe first output shaft gear and a second gear part that engages thesecond output shaft gear; and

a gear train configured to couple the first relay transmission gear andthe second relay transmission gear in an interlocked manner.

According to this configuration, when the first input shaft gear iscoupled in an interlocked manner to the input shaft and the first outputshaft gear is coupled in an interlocked manner to the output shaft, thepower of the input shaft is transmitted to the output shaft via thefirst input shaft gear, the first relay transmission gear, the geartrain, the second relay transmission gear and the first output shaftgear, and transmitted to the power take-off shaft from the output shaft.When the first input shaft gear is coupled in an interlocked manner tothe input shaft and the second output shaft gear is coupled in aninterlocked manner to the output shaft, the power of the input shaft istransmitted to the output shaft via the first input shaft gear, thefirst relay transmission gear, the gear train, the second relaytransmission gear and the second output shaft gear, and transmitted tothe power take-off shaft from the output shaft. When the second inputshaft gear is coupled in an interlocked manner to the input shaft andthe first output shaft gear is coupled in an interlocked manner to theoutput shaft, the power of the input shaft is transmitted to the outputshaft via the second input shaft gear, the first relay transmissiongear, the gear train, the second relay transmission gear and the firstoutput shaft gear, and transmitted to the power take-off shaft from theoutput shaft. When the second input shaft gear is coupled in aninterlocked manner to the input shaft and the second output shaft gearis coupled in an interlocked manner to the output shaft, the power ofthe input shaft is transmitted to the output shaft via the second inputshaft gear, the first relay transmission gear, the gear train, thesecond relay transmission gear and the second output shaft gear, andtransmitted to the power take-off shaft from the output shaft.

Power also passes through the gear train in the case of shifting thepower of the input shaft at one of the four speed levels andtransmitting resultant power to the output shaft, and thus, even when,for example, the rotation speed of the power that is input to the inputshaft changes, as long as the speed/transmission ratio of the gear trainis appropriately changed, the power take-off shaft is driven at anunchanged rotation speed in each the four speed levels, without changingany of the first input shaft gear, the second input shaft gear, thefirst relay transmission gear, the second relay transmission gear, thefirst output shaft gear or the second output shaft gear. Also, evenwhen, for example, the rotation speed of the power that is input to theinput shaft does not change, as long as the speed/transmission ratio ofthe gear train is changed, the power take-off shaft is driven at achanged rotation speed in each of the four speed levels, withoutchanging any of the first input shaft gear, the second input shaft gear,the first relay transmission gear, the second relay transmission gear,the first output shaft gear or the second output shaft gear.

In other words, the rotation speed of the power take-off shaft at eachof the four speed levels can be adjusted easily and cost effectively bysimply changing the gears of the gear train.

In one preferred embodiment, the gear train has only a first relay gearthat is coupled in an interlocked manner to the first relay transmissiongear, and a second relay gear that is coupled in an interlocked mannerto the second relay transmission gear in a state of engaging the firstrelay gear. According to this configuration, the structure of the geartrain is realized with a simple structure that is only provided with afirst relay gear and a second relay gear.

In one preferred embodiment, the first relay gear and the first andsecond gear parts of the first relay transmission gear are supported bythe same first relay shaft, and the second relay gear and the first andsecond gear parts of the second relay transmission gear are supported bythe same second relay shaft. According to this configuration, thestructure of the power take-off apparatus is realized with a simplestructure that is only provided with a total of four shafts, namely, theinput shaft, the first relay shaft, the second relay shaft, and theoutput shaft.

In one preferred embodiment, the first relay shaft and the second relayshaft extend in the vehicle body longitudinal direction, and the geartrain is provided spanning a region of the first relay shaft that islocated on the rear side with respect to the first and second gear partsof the first relay transmission gear and a region of the second relayshaft that is located on the rear side with respect to the first andsecond gear parts of the second relay transmission gear. According tothis configuration, the gear train can be removed rearwardly of thefirst relay transmission gear and the second relay transmission gear,thus facilitating easy replacement of the gear train.

(4) Further features of the present invention and advantages thereofwill become apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment (same through to FIG. 7), and is a leftside view showing the entirety of a tractor serving as an example of awork vehicle;

FIG. 2 is a diagram showing a power transmission structure;

FIG. 3 is a side view in vertical section of a power take-off apparatus;

FIG. 4 is a diagram showing the power take-off apparatus;

FIG. 5 is a right side view showing operation parts for shifting;

FIG. 6 is a rear view showing operation parts for shifting;

FIG. 7 is a view in section showing a rear-wheel driving part;

FIG. 8 shows a second embodiment (same through to FIG. 11), and is aleft side view showing the entirety of a tractor serving as an exampleof a work vehicle;

FIG. 9 is a diagram showing a power transmission structure;

FIG. 10 is a view in section of the power take-off apparatus in anexpanded state; and

FIG. 11 is a diagram of a power take-off apparatus provided with acomparative structure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, in relation to a traveling vehicle body ofa tractor (example of “work vehicle”), the direction of arrow F shown inFIG. 1 is “forward of the vehicle body”, the direction of arrow B is“rearward of the vehicle body”, the direction of arrow U is “upward ofthe vehicle body”, the direction of arrow D is “downward of the vehiclebody”, the direction on the near side of the page is “leftward of thevehicle body”, and the direction on the far side of the page is“rightward of the vehicle body”.

First Embodiment Overall Configuration of Tractor

As shown in FIG. 1, the tractor is provided with a traveling vehiclebody 3 steerably and drivably equipped with a right and left pair offront wheels 1, and drivably equipped with a right and left pair of rearwheels 2. A prime mover part 5 having an engine 4 is formed in a frontportion of the traveling vehicle body 3. A driving part 8 having adriver's seat 6 and a steering wheel 7 for steering the front wheels 1is formed in a rear portion of the traveling vehicle body 3. The drivingpart 8 is provided with a cabin 9 covering an occupant space. A linkmechanism 10 for coupling various types of work apparatuses such as arotary tilling apparatus (not shown) to the tractor in a liftablyoperable manner and a power take-off apparatus 40 that takes off powerfrom the engine 4 with a power take-off shaft 41 and outputs resultantpower to the coupled work apparatus (apparatus to be driven) areprovided in a rear portion of the traveling vehicle body 3. A vehiclebody frame of the traveling vehicle body 3 is constituted by atransmission case 11 that is coupled at a front portion to a rearportion of the engine 4 and supports the rear wheels 2 and a front wheelsupport frame 12 that is coupled to a lower portion of the engine 4 andsupports the front wheels 1.

Configuration of Power Transmission

The power of the engine 4 is transmitted to the front wheels 1, the rearwheels 2 and the power take-off shaft 41 based on the power transmissionstructure shown in FIG. 2.

That is, the power of an engine output shaft 4 a of the engine 4 istransmitted to a transmission input shaft 11 a of the transmission case11. The power of the transmission input shaft 11 a is input to aforward/reverse switching apparatus 13 and converted into forward powerand reverse power.

The forward power and reverse power obtained through conversion areinput to an 8-speed main transmission apparatus 14 and undergo maintransmission, and the forward power and reverse power that haveundergone main transmission are input to a 2-speed creep transmissionapparatus 15. The output of the creep transmission apparatus 15 is inputto a 3-speed auxiliary transmission apparatus 16 and undergoes auxiliarytransmission. The power obtained through auxiliary transmission is inputto a rear wheel differential mechanism 17 and transmitted to the rightand left rear wheels 2 from right and left output shafts 17 a of therear wheel differential mechanism 17. The power from the auxiliarytransmission apparatus 16 is transmitted to a front wheel transmissionapparatus 20 via the input shaft 17 b of the rear wheel differentialmechanism 17, is transmitted to a front wheel differential mechanism 21from the front wheel transmission apparatus 20, and is transmitted tothe right and left front wheels 1 from the front wheel differentialmechanism 21. The front wheel transmission apparatus 20 is configured tobe switchable between an OFF state, a uniform speed transmission stateand an acceleration transmission state. The front wheel transmissionapparatus 20, when switched to the OFF state, cuts off output to thefront wheel differential mechanism 21, and the tractor enters atwo-wheel drive state in which only the rear wheels 2 are driven out ofthe front wheels 1 and the rear wheels 2. The front wheel transmissionapparatus 20, when switched to the uniform speed transmission state,outputs the power from the input shaft 17 b to the front wheeldifferential mechanism 21 in the uniform speed state, and the tractorenters a four-wheel drive state in which the front wheels 1 and the rearwheels 2 are driven in a state where the average circumferential speedof the right and left front wheels 1 is substantially equal the averagecircumferential speed of the right and left rear wheels 2. The frontwheel transmission apparatus 20, when switched to the accelerationtransmission state, upshifts the power from the input shaft 17 b andoutputs resultant power to the front wheel differential mechanism 21,and the tractor enters a four-wheel drive state in which the frontwheels 1 and the rear wheels 2 are driven in a state where the averagecircumferential speed of the right and left front wheels 1 is fasterthan the average circumferential speed of the right and left rear wheels2.

The power of the transmission input shaft 11 a is transmitted to a workclutch 24 via a front rotation shaft 22 coupled at a front end portionto a rear end portion of the transmission input shaft 11 a and a rearrotation shaft 23 coupled at a front end portion to a rear end portionof the front rotation shaft 22, and transmitted to the power take-offapparatus 40 from the work clutch 24.

Configuration of Power Take-Off Apparatus

The power take-off apparatus 40 is, as shown in FIG. 1, provided in arear portion of the traveling vehicle body 3. The power take-offapparatus 40 is, as shown in FIG. 3, provided with a power take-off case42 formed in a rear portion of the transmission case 11. The powertake-off case 42 is constituted by the transmission case 11 and a gearcase 42 a removably attached to a rear wall part 11 b of thetransmission case 11 in a state of closing an opening formed in the rearwall part 11 b. The power take-off shaft 41 protrudes rearward from avertically intermediate portion of the gear case 42 a. In FIG. 3, thepower take-off shaft 41 is covered by a cover 41 a removably attached tothe gear case 42 a.

As shown in FIGS. 3 and 4, an input shaft 43 is provided in an upperportion of an interior space S of the power take-off case 42 in a stateof extending in the vehicle body longitudinal direction. The input shaft43 is rotatably supported by the gear case 42 a and a supporting wallpart 44 located forward of the gear case 42 a. The supporting wall part44 is coupled to the gear case 42 a via a coupling rod part (not shown)that extends rearward from a plurality of places of a peripheral portionof the supporting wall part 44, and is supported by the gear case 42 a.A front portion of the input shaft 43 is coupled in an interlockedmanner to an output member 24 a of the work clutch 24. The power of thetransmission input shaft 11 a, that is, the power of the engine 4, istransmitted to the input shaft 43.

An output shaft 45 that extends in the vehicle body longitudinaldirection in parallel with the input shaft 43 is provided downward ofthe input shaft 43. The output shaft 45 is rotatably supported by thegear case 42 a and the supporting wall part 44. The output shaft 45 iscoupled in an interlocked manner to the power take-off shaft 41 byspline engagement with a rear portion of the output shaft 45 and a frontportion of the power take-off shaft 41. It is possible to take off thepower of the output shaft 45 with the power take-off shaft 41.

A first gear train 46 is provided spanning the front portion of theinput shaft 43 and the front portion of the output shaft 45. The firstgear train 46 has only two gears, namely, a first input shaft gear 46Arelatively rotatably supported by the input shaft 43 and a first outputshaft gear 46B relatively rotatably supported by the output shaft 45 ina state of engaging the first input shaft gear 46A. Backward of thefirst gear train 46, a second gear train 47 is provided spanning and theinput shaft 43 and the output shaft 45. The second gear train 47 hasonly two gears, namely, a second input shaft gear 47A relativelyrotatably supported by the input shaft 43 and a second output shaft gear47B relatively rotatably supported by the output shaft 45 in a state ofengaging the second input shaft gear 47A. The first output shaft gear46B is supported by the output shaft 45 via a taper roller bearing 48interposed between the output shaft 45 and a boss part of the firstoutput shaft gear 46B. The second output shaft gear 47B is supported bythe output shaft 45 via a taper roller bearing 48 interposed between theoutput shaft 45 and a boss part of the second output shaft gear 47B. Thetaper roller bearing 48 of the first output shaft gear 46B and the taperroller bearing 48 of the second output shaft gear 47B are provided withtwo rows of rollers in an outward facing state.

The outer diameter of the second input shaft gear 47A is configured tobe larger than the outer diameter of the first input shaft gear 46A. Theouter diameter of the first output shaft gear 46B is configured to belarger than the outer diameter of the first input shaft gear 46A. Theouter diameter of the second output shaft gear 47B is configured to belarger than the outer diameter of the second input shaft gear 47A. Theouter diameter of the second output shaft gear 47B is configured to besmaller than the outer diameter of the first output shaft gear 46B. Afirst speed/transmission ratio Z1 of the first gear train 46 differsfrom a second speed/transmission ratio Z2 of the second gear train 47.

As shown in FIGS. 3 and 4, an input shaft sleeve 50 is relativelyrotatably and slidably supported by the input shaft 43, between thefirst input shaft gear 46A and the second input shaft gear 47A. Theinput shaft sleeve 50, when slid to the first input shaft gear side,engages a latch part 46 c that is formed on a side portion of the firstinput shaft gear 46A, and couples the first input shaft gear 46A to theinput shaft 43 in an interlocked manner. The input shaft sleeve 50, whenslid to the second input shaft gear side, engages the latch part 47 cthat is formed on a side portion of the second input shaft gear 47A, andcouples the second input shaft gear 47A to the input shaft 43 in aninterlocked manner.

As shown in FIGS. 3, 5 and 6, a first operation part 53 thatalternatively couples the first input shaft gear 46A and the secondinput shaft gear 47A to the input shaft 43 in an interlocked manner isconstituted by a first shift fork 51 that engages the input shaft sleeve50, a first transmission arm 52 swingably provided outside the powertake-off case 42, and the like. The first shift fork 51 and the firsttransmission arm 52 are coupled in an interlocked manner via a slideshaft 54 that slidably operates the first shift fork 51, a swinging arm55 that engages the slide shaft 54 at a free end portion, and a rotationshaft 56 that swingably supports the swinging arm 55 and the firsttransmission arm 52.

In operation of the first operation part 53, the first shift fork 51 isslidably operated in the direction along the axis of the input shaft 43,in response to the first transmission arm 52 being swingably operatedwith the axis of the rotation shaft 56 as the swing fulcrum, and thefirst shift fork 51 couples the first input shaft gear 46A to the inputshaft 43 in an interlocked manner by engaging the input shaft sleeve 50with the first input shaft gear 46A, and the first shift fork 51 couplesthe second input shaft gear 47A to the input shaft 43 in an interlockedmanner by engaging the input shaft sleeve 50 with the second input shaftgear 47A.

As shown in FIGS. 3 and 4, an output shaft sleeve 60 is relativelyrotatably and slidably supported by the output shaft 45, between thefirst output shaft gear 46B and the second output shaft gear 47B. Theoutput shaft sleeve 60, when slid to the first output shaft gear side,couples the first output shaft gear 46B to the output shaft 45 in aninterlocked manner by engaging the latch part 46 d that is formed on aside portion of the first output shaft gear 46B. The output shaft sleeve60, when slid to the second output shaft gear side, couples the secondoutput shaft gear 47B to the output shaft 45 in an interlocked manner byengaging the latch part 47 d that is formed on a side portion of thesecond output shaft gear 47B.

As shown in FIGS. 3, 5 and 6, a second operation part 63 thatalternatively couples the first output shaft gear 46B and the secondoutput shaft gear 47B to the output shaft 45 in an interlocked manner isconstituted by a second shift fork 61 that engages an output shaftsleeve 60, a second transmission arm 62 provided to be swingablyoperable outside the power take-off case 42, and the like. The secondshift fork 61 and the second transmission arm 62 are coupled in aninterlocked manner via a slide shaft 64 that slidably operates thesecond shift fork 61, a swinging arm 65 that engages the slide shaft 64at a free end portion, and a rotation shaft 66 that swingably supportsthe swinging arm 65 and the second transmission arm 62.

In operation of the second operation part 63, the second shift fork 61is slidably operated in the direction along the axis of the output shaft45, in response to the second transmission arm 62 being swingablyoperated with the axis of the rotation shaft 66 as the swing fulcrum,and the second shift fork 61 couples the first output shaft gear 46B tothe output shaft 45 in an interlocked manner by engaging the outputshaft sleeve 60 with the first output shaft gear 46B, and the secondshift fork 61 couples the second output shaft gear 47B to the outputshaft 45 in an interlocked manner by engaging the output shaft sleeve 60with the second output shaft gear 47B.

The first operation part 53 and the second operation part 63 are, asshown in FIG. 5, operated by a single shifter 67 that is linked to thefirst transmission arm 52 and the second transmission arm 62. That is,the shifter 67 is configured to be switchable between a state of beinglinked to the first transmission arm 52 in which the first transmissionarm 52 becomes swingably operable and a state of being linked to thesecond transmission arm 62 in which the second transmission arm 62becomes swingably operable.

As shown in FIGS. 3 and 4, a relay transmission shaft 70 extending inthe vehicle body longitudinal direction in parallel with the outputshaft 45 is provided downward of the output shaft 45. The relaytransmission shaft 70 is rotatably supported by the gear case 42 a andthe supporting wall part 44. As shown in FIG. 6, when viewed in thevehicle body longitudinal direction, the input shaft 43, the outputshaft 45 and relay transmission shaft 70 are positioned on a straightline in the vehicle body vertical direction. The relay transmissionshaft 70, as shown in FIGS. 3 and 4, is coupled in an interlocked mannerto the first output shaft gear 46B by the first relay transmission gearmechanism 71 provided on a front portion of the relay transmission shaft70, and is coupled in an interlocked manner to the second output shaftgear 47B by a second relay transmission gear mechanism 72 provided on arear portion of the relay transmission shaft 70. The first gear train 46and the first relay transmission gear mechanism 71 are provided on aside surface of the vehicle body in a single file state on a straightline extending in the vehicle body vertical direction through which passthe axis of the input shaft 43, the axis of the output shaft 45 and theaxis of the relay transmission shaft 70. The second gear train 47 andthe second relay transmission gear mechanism 72 are provided on a sidesurface of the vehicle body in a single file state on a straight lineextending in the vehicle body vertical direction through which pass theaxis of the input shaft 43, the axis of the output shaft 45, and theaxis of the relay transmission shaft 70. The first relay transmissiongear mechanism 71 is constituted by a first relay transmission gearrelatively non-rotatably supported by the relay transmission shaft 70 astate of engaging the first output shaft gear 46B. The second relaytransmission gear mechanism 72 is constituted by a second relaytransmission gear relatively non-rotatably supported by the relaytransmission shaft 70 in a state of engaging the second output shaftgear 47B.

The outer diameter of the first relay transmission gear is configured tobe smaller than the outer diameter of the first output shaft gear 46B.The outer diameter of the second relay transmission gear is configuredto be smaller than the outer diameter of the second output shaft gear47B. The outer diameter of the second relay transmission gear isconfigured to be larger than the outer diameter of the first relaytransmission gear. The first relay speed/transmission ratio Y1 of thefirst relay transmission gear mechanism 71 differs from the second relayspeed/transmission ratio Y2 of the second relay transmission gearmechanism 72.

A gear shift mechanism M that shifts the power of the input shaft 43 totransmission power having four different rotation speeds and transmitsresultant power to the output shaft 45 is constituted by the first geartrain 46, the second gear train 47, the input shaft sleeve 50, theoutput shaft sleeve 60, the relay transmission shaft 70, the first relaytransmission gear mechanism 71, and the second relay transmission gearmechanism 72. In the power take-off apparatus 40, in response to thefirst input shaft gear 46A and the second input shaft gear 47A beingalternatively coupled in an interlocked manner to the input shaft 43 bythe first operation part 53, and the first output shaft gear 46B and thesecond output shaft gear 47B being alternatively coupled in aninterlocked manner to the output shaft 45 by the second operation part63, the gear shift mechanism M switches between a first transmissionstate, a second transmission state, a third transmission state and afourth transmission state, and the rotation speed of the power take-offshaft 41 is changed through four steps.

That is, when the first input shaft gear 46A is coupled in aninterlocked manner to the input shaft 43 in response to operation of theinput shaft sleeve 50 by the first operation part 53, and the firstoutput shaft gear 46B is coupled in an interlocked manner to the outputshaft 45 in response to operation of the output shaft sleeve 60 by thesecond operation part 63, the gear shift mechanism M enters the firsttransmission state. The gear shift mechanism M in the first transmissionstate transmits the power of the input shaft 43 to the output shaft 45via the first gear train 46, and the power take-off shaft 41 is drivenat a rotation speed that is set by the first transmission state.

When the second input shaft gear 47A is coupled in an interlocked mannerto the input shaft 43 in response to operation of the input shaft sleeve50 by the first operation part 53 and the second output shaft gear 47Bis coupled in an interlocked manner to the output shaft 45 in responseto operation of the output shaft sleeve 60 by the second operation part63, the gear shift mechanism M enters the second transmission state. Thegear shift mechanism M in the second transmission state transmits thepower of the input shaft 43 to the output shaft 45 via the second geartrain 47, and the power take-off shaft 41 is driven at a rotation speedthat is set by the second transmission state.

When the first input shaft gear 46A is coupled in an interlocked mannerto the input shaft 43 in response to operation of the input shaft sleeve50 by the first operation part 53 and the second output shaft gear 47Bis coupled in an interlocked manner to the output shaft 45 in responseto operation of the output shaft sleeve 60 by the second operation part63, the gear shift mechanism M enters the third transmission state. Thegear shift mechanism M in the third transmission state transmits thepower of the input shaft 43 to the output shaft 45 via the first geartrain 46, the first relay transmission gear mechanism 71, the relaytransmission shaft 70, the second relay transmission gear mechanism 72and the second output shaft gear 47B, and the power take-off shaft 41 isdriven at a rotation speed that is set by the third transmission state.At this time, the first output shaft gear 46B is supported by the outputshaft 45 to which the drive load of the power take-off shaft 41 isapplied, while being relatively rotatable with respect to the outputshaft 45, and, because of being supported via the taper roller bearing48, performs power transmission while rotating smoothly.

When the second input shaft gear 47A is coupled in an interlocked mannerto the input shaft 43 in response to operation of the input shaft sleeve50 by the first operation part 53 and the first output shaft gear 46B iscoupled in an interlocked manner to the output shaft 45 in response tooperation of the output shaft sleeve 60 by the second operation part 63,the gear shift mechanism M enters the fourth transmission state. Thegear shift mechanism M in the fourth transmission state transmits thepower of the input shaft 43 to the output shaft 45 via the second geartrain 47, the second relay transmission gear mechanism 72, the relaytransmission shaft 70, the first relay transmission gear mechanism 71and the first output shaft gear 46B, and the power take-off shaft 41 isdriven at a rotation speed that is set by the fourth transmission state.At this time, the second output shaft gear 47B is supported by theoutput shaft 45 to which the drive load of the power take-off shaft 41is applied, while being relatively rotatably with respect to the outputshaft 45, and, because of being supported via the taper roller bearing48, performs power transmission while rotating smoothly.

Drive Structure of Rear Wheels

As shown in FIG. 7, a brake case part 75 is provided on a side portionof the transmission case 11, and an axle case 76 extends laterallyoutward of the vehicle body from the brake case part 75. A reductioncase part 77 is provided on a base portion of the axle case 76.

The rear wheel differential mechanism 17 is provided inside thetransmission case 11. The output shaft 17 a of the rear wheeldifferential mechanism 17 extends from a side gear 79 to inside thereduction case part 77. A rear wheel axle 80 is rotatably supportedinside the axle case 76 in a state of being located on the vehicle bodylateral outer side of the rear wheel differential mechanism 17. Theoutput shaft 17 a and the rear wheel axle 80 are provided in a state ofbeing located on the same axis. A locking apparatus 82 that enablesdifferential locking of the rear wheel differential mechanism 17 isprovided spanning the side gear 79 and a differential case 81.

Inside the reduction case part 77, a planetary reduction mechanism 83 isprovided spanning the output shaft 17 a and the rear wheel axle 80. Theplanetary reduction mechanism 83 has a sun gear 83 a that is driven bythe output shaft 17 a, an internal gear 83 b that is supported by thereduction case part 77, and a plurality of planet gears 83 c that arealigned in the circumferential direction of the sun gear 83 a. A carrier83 d that supports the plurality of planet gears 83 c is coupled to therear wheel axle 80. A stopper 83 e that prevents the carrier 83 d fromcoming off the rear wheel axle 80 is mounted to the rear wheel axle 80with a bolt 84.

In the rear wheel differential mechanism 17, the power of the inputshaft 17 b is transmitted to the output shaft 17 a via the differentialcase 81 and the side gear 79. The power of the output shaft 17 a istransmitted to the rear wheel axle 80 after being downshifted by theplanetary reduction mechanism 83 and drives the rear wheel axle 80, andthe rear wheels 2 are driven by the rear wheel axle 80.

A brake 85 is provided inside the brake case part 75. The brake 85 has aplurality of friction plates 86 latched to a region of the output shaft17 a between the differential case 81 of the rear wheel differentialmechanism 17 and the planetary reduction mechanism 83, and a pluralityof friction plates 88 latched to a support part 87 provided on the brakecase part 75. A friction plate receiving part 89 that receives thefriction plates 86 and the friction plates 88 is provided on the side onwhich the planetary reduction mechanism 83 is located with respect tothe friction plates 86 and the friction plates 88. The friction platereceiving part 89 is fixed to the brake case part 75. A hydraulic piston90 is provided on an opposite side to the side on which the frictionplate receiving part 89 is located with respect to the friction plates86 and friction plates 88.

As shown in FIG. 7, the output shaft 17 a is configured to be supportedbetween the differential case 81 and the planetary reduction mechanism83 by a support member 91. The support member 91 is configured to engagethe output shaft 17 a relatively immovably in the direction along theaxis of the output shaft 17 a.

Specifically, as shown in FIG. 7, the support member 91 is mounted in aregion of the output shaft 17 a between the friction plates 86 that arelatched to the output shaft 17 a and the planetary reduction mechanism83. The support member 91 is constituted by a bearing provided with aninner ring 91 a fitted onto the output shaft 17 a, an outer ring 91 bthat fits into an attachment hole formed in the friction plate receivingpart 89, and a rolling body 91 c interposed between the inner ring 91 aand the outer ring 91 b. The support member 91 relatively immovablyengages the output shaft 17 a by friction between the inner ring 91 aand the output shaft 17 a. The support member 91 is supported by thebrake case part 75 by being supported by the friction plate receivingpart 89.

In operation of the brake 85, in response to operating hydraulicpressure being supplied to the hydraulic piston 90, the brake enters anON state and is applied to the rear wheels 2, and in response tocancelling supply of operating hydraulic pressure to the hydraulicpiston 90, the brake enters an OFF state and is released from the rearwheels 2.

That is, when operating hydraulic pressure is supplied to the hydraulicpiston 90, the hydraulic piston 90 is pressed toward the friction plates86 by the operating hydraulic pressure, the friction plates 86 and thefriction plates 88 are pressed in the direction along the axis of theoutput shaft 17 a by the hydraulic piston 90 and pressed against thefriction plate receiving part 89, and friction braking power generatedby the friction plates 86 and the friction plates 88 is applied to therear wheel axle 80 via the output shaft 17 a and the planetary reductionmechanism 83.

When supply of the operating hydraulic pressure to the hydraulic piston90 is canceled, the pressing of the hydraulic piston 90 toward thefriction plates 86 is released, the pressing of the friction plates 86and the friction plates 88 against the friction plate receiving part 89is released, and generation of friction braking power by the frictionplates 86 and the friction plates 88 is canceled.

For example, when the brake 85 is operated to an ON state, the outputshaft 17 a is prevented from moving together with the friction plates 86by the support member 91, and after the brake 85 has returned to an OFFstate, the friction plates 86 of the output shaft 17 a and the frictionplates 88 of the support part 87 remaining in contact and rotationresistance being applied to the output shaft 78 can be avoided.

Other Embodiments of the First Embodiment

(1) In the embodiment described above, the rear wheels 2 are driven, butthe present invention is not limited thereto, and the front wheels maybe driven.

(2) In the embodiment described above, the support member 91 is providedin a region of the output shaft 17 a between the brake 85 and theplanetary reduction mechanism 83, but the present invention is notlimited thereto, and the support member 91 may be provided in a regionof the output shaft 17 a between the rear wheel differential mechanism17 (wheel differential mechanism) and the brake 85.

(3) In the embodiment described above, the support member 91 is abearing, but the present invention is not limited thereto. For example,it is possible to employ a bushing or impregnated metal.

(4) In the embodiment described above, the bearing is supported by thefriction plate receiving part 89, but the present invention is notlimited thereto, and a dedicated holder supporting the bearing may beprovided.

(5) In the embodiment described above, the first gear train 46 and thesecond gear train 47 have only two gears, but these gear trains may havethree or more gears. Also, the first relay transmission gear mechanism71 and the second relay transmission gear mechanism 72 have only onegear, but these relay transmission gear mechanisms may have two or moregears.

(6) In the embodiment described above, the input shaft 43, the outputshaft 45 and the relay transmission shaft 70 are provided in state ofbeing positioned on a straight line extending in the vehicle bodyvertical direction when viewed in the vehicle body longitudinaldirection. Instead thereof, the input shaft 43 and the output shaft 45may be positioned on a straight line extending in the vehicle bodyvertical direction, and the relay transmission shaft 70 may be shiftedlaterally with respect to the input shaft 43 and the output shaft 45, orthe input shaft 43 and the relay transmission shaft 70 may be positionedon a straight line extending in the vehicle body vertical direction, andthe output shaft 45 may be shifted laterally with respect to the inputshaft 43 and the relay transmission shaft 70, or the input shaft 43, theoutput shaft 45 and the relay transmission shaft 70 may deviate from astraight line extending in the vehicle body vertical direction, forexample.

(7) In the embodiment described above, the first output shaft gear 46Band the second output shaft gear 47B are supported by the output shaft45 via the taper roller bearing 48, but the present invention is notlimited thereto. For example, it is possible to employ a ball bearing ora needle bearing.

Second Embodiment Overall Configuration of Tractor

As shown in FIG. 8, the tractor is provided with a traveling vehiclebody 103 steerably and drivably equipped with a right and left pair offront wheels 101 and drivably equipped with a right and left pair ofrear wheels 102. A prime mover part 105 having an engine 104 is formedin a front portion of the traveling vehicle body 103. A driving part 108having a driver's seat 106 and a steering wheel 107 for steering thefront wheels 101 is formed in a rear portion of the traveling vehiclebody 103. The driving part 108 is provided with a cabin 109 that coversan occupant space. A link mechanism 110 for coupling various types ofwork apparatuses such as a rotary tilling apparatus (not shown) to thetractor in a liftably operable manner and a power take-off apparatus 130that takes off power from the engine 104 with a power take-off shaft 131and outputs resultant power to the coupled work apparatus (apparatus tobe driven) are provided in a rear portion of the traveling vehicle body103. A vehicle body frame of the traveling vehicle body 103 isconstituted by a transmission case 111 that is coupled at a frontportion to a rear portion of the engine 104 and supports the rear wheels102 and a front wheel support frame 112 that is coupled to a lowerportion of the engine 104 and supports the front wheels 101.

Configuration of Power Transmission

The power of the engine 104 is transmitted to the front wheels 101, therear wheels 102 and the power take-off shaft 131 based on the powertransmission structure shown in FIG. 9.

That is, the power of an engine output shaft 104 a of the engine 104 istransmitted to a transmission input shaft 111 a of the transmission case111. The power of the transmission input shaft 111 a is input to aforward/reverse switching apparatus 113 and converted into forward powerand reverse power. The forward power and reverse power obtained throughconversion are input to an 8-speed main transmission apparatus 114 andundergo main transmission, and the forward power and reverse power thathave undergone main transmission are input to a 2-speed creeptransmission apparatus 115. The output of the creep transmissionapparatus 115 is input to a 3-speed auxiliary transmission apparatus 116and undergoes auxiliary transmission. The power obtained throughauxiliary transmission is input to a rear wheel differential mechanism117, and transmitted to the right and left rear wheels 102 from rightand left output shafts 117 a of the rear wheel differential mechanism117. A handbrake 118 and a planetary reduction mechanism 119 areprovided in the transmission system from the rear wheel differentialmechanism 117 to the rear wheels 102. The power from the auxiliarytransmission apparatus 116 is transmitted to a front wheel transmissionapparatus 120 via the input shaft 117 b of the rear wheel differentialmechanism 117, is transmitted to a front wheel differential mechanism121 from the front wheel transmission apparatus 120, and is transmittedto the right and left front wheels 101 from the front wheel differentialmechanism 121. The front wheel transmission apparatus 120 is configuredto be switchable between an OFF state, a uniform speed transmissionstate, and an acceleration transmission state. The front wheeltransmission apparatus 120, when switched to the OFF state, cuts offoutput to the front wheel differential mechanism 121, and the tractorenters a two-wheel drive state in which only the rear wheels 102 aredriven out of the front wheels 101 and the rear wheels 102. The frontwheel transmission apparatus 120, when switched to the uniform speedtransmission state, outputs the power from the input shaft 117 b to thefront wheel differential mechanism 121 in the uniform speed state, andthe tractor enters a four-wheel drive state in which the front wheels101 and the rear wheels 102 are driven in a state where the averagecircumferential speed of the right and left front wheels 101 issubstantially equal the average circumferential speed of the right andleft rear wheels 102. The front wheel transmission apparatus 120, whenswitched to the acceleration transmission state, upshifts the power fromthe input shaft 117 b and outputs resultant power to the front wheeldifferential mechanism 121, and the tractor enters a four-wheel drivestate in which the front wheels 101 and the rear wheels 102 are drivenin a state where the average circumferential speed of the right and leftfront wheels 101 is faster than the average circumferential speed of theright and left rear wheels 102.

The power of the transmission input shaft 111 a is transmitted to a workclutch 124 via a front rotation shaft 122 coupled at a front end portionto a rear end portion of the transmission input shaft 111 a and a rearrotation shaft 123 coupled at a front end portion to a rear end portionof the front rotation shaft 122, and transmitted to the power take-offapparatus 130 from the work clutch 124.

Configuration of Power Take-Off Apparatus

The power take-off apparatus 130 is, as shown in FIG. 8, provided in arear portion of the traveling vehicle body 103. The power take-offapparatus 130 is, as shown in FIG. 10, provided with a power take-offcase 132 formed in a rear portion of the transmission case 111. Thepower take-off case 132 is constituted by the transmission case 111 anda gear case 132 a removably attached to a rear wall part 111 b of thetransmission case 111 in a state of closing an opening formed in therear wall part 111 b. The power take-off shaft 131 protrudes rearwardfrom a lower portion of the gear case 132 a.

As shown in FIG. 10, an input shaft 133 is provided in an upper portionof an interior space S of the power take-off case 132 in a state ofextending in the vehicle body longitudinal direction. The input shaft133 is rotatably supported by the gear case 132 a and a supporting wallpart 134 located forward of the gear case 132 a. The supporting wallpart 134 is coupled to the gear case 132 a via a coupling rod part (notshown) that extends rearward from a plurality of places of a peripheralportion of the supporting wall part 134, and is supported by the gearcase 132 a. A front portion of the input shaft 133 is coupled in aninterlocked manner to an output member of the work clutch 124. The powerof the transmission input shaft 111 a, that is, the power of the engine104, is transmitted to the input shaft 133.

A first input shaft gear 135 is relatively rotatably supported by theinput shaft 133. A second input shaft gear 136 is relatively rotatablysupported by the input shaft 133 on a rear side with respect to thefirst input shaft gear 135. The first input shaft gear 135 and thesecond input shaft gear 136 are configured such that the diameter of thefirst input shaft gear 135 differs from the diameter of the second inputshaft gear 136. In the present embodiment, the diameter of the firstinput shaft gear 135 is configured to be larger than the diameter of thesecond input shaft gear 136.

An input shaft sleeve 137 is relatively rotatably and slidably supportedby the input shaft 133, between the first input shaft gear 135 and thesecond input shaft gears 136. The input shaft sleeve 137 switchesbetween a state of engaging a latch part 135 a that is formed on a sideportion of the first input shaft gear 135 and a state of engaging alatch part 136 a that is formed on a side portion of the second inputshaft gear 136, in response to the input shaft sleeve 137 being slidablyoperated by a first shift fork 138 that is engaging a peripheral portionof the input shaft sleeve 137. When the input shaft sleeve 137 engagesthe latch part 135 a of the first input shaft gear 135, the first inputshaft gear 135 is coupled in an interlocked manner to the input shaft133, and when the input shaft sleeve 137 engages the latch part 136 a ofthe second input shaft gear 136, the second input shaft gear 136 iscoupled in an interlocked manner to the input shaft 133. The first inputshaft gear 135 and the second input shaft gear 136 are alternativelycoupled in an interlocked manner to the input shaft 133 by the inputshaft sleeve 137.

An output shaft 140 that is parallel with the input shaft 133 isprovided downward of the input shaft 133 in a state of extending in thevehicle body longitudinal direction. The output shaft 140 is rotatablysupported by the gear case 132 a and the supporting wall part 134. Theoutput shaft 140 is coupled in an interlocked manner to the powertake-off shaft 131 by spline engagement with a rear portion 140 a of theoutput shaft 140 and a front portion 131 a of the power take-off shaft131. It is possible to take off the power of the output shaft 140 withthe power take-off shaft 131.

A first output shaft gear 141 is relatively rotatably supported by theoutput shaft 140. A second output shaft gear 142 is relatively rotatablysupported by the output shaft 140 on a rear side with respect to thefirst output shaft gear 141. The first output shaft gear 141 and thesecond output shaft gear 142 are configured such that the diameter ofthe first output shaft gear 141 differs from the diameter of the secondoutput shaft gear 142. In the present embodiment, the diameter of thefirst output shaft gear 141 is configured to be larger than the diameterof the second output shaft gear 142.

An output shaft sleeve 143 is relatively rotatably and slidablysupported by the output shaft 140, between the first output shaft gear141 and the second output shaft gears 142. The output shaft sleeve 143switches between a state of engaging a latch part 141 a that is formedon a side portion of the first output shaft gear 141 and a state ofengaging a latch part 142 a that is formed on a side portion of thesecond output shaft gear 142, in response to the output shaft sleeve 143being slidably operated by the second shift fork 144 that is engaging aperipheral portion of the output shaft sleeve 143. When the output shaftsleeve 143 engages the latch part 141 a of the first output shaft gear141, the first output shaft gear 141 is coupled in an interlocked mannerto the output shaft 140, and when the output shaft sleeve 143 engagesthe latch part 142 a of the second output shaft gear 142, the secondoutput shaft gear 142 is coupled in an interlocked manner to the outputshaft 140. The first output shaft gear 141 and the second output shaftgear 142 are alternatively coupled in an interlocked manner to theoutput shaft 140 by the output shaft sleeve 143.

A first relay transmission gear 145 and a second relay transmission gear146 are provided between the input shaft 133 and the output shaft 140.The first relay transmission gear 145 has a first gear part 145 a thatengages the first input shaft gear 135, a second gear part 145 b thatengages the second input shaft gear 136, and a first relay shaft 145 cthat supports the first gear part 145 a and the second gear part 145 b.The first relay shaft 145 c is engaged by spline engagement with thefirst gear part 145 a and the second gear part 145 b, and doubles as acoupling member that couples the first gear part 145 a and the secondgear part 145 b in an interlocked manner. The first relay shaft 145 c isrotatably supported by the gear case 132 a and the supporting wall part134 in a state of extending in the vehicle body longitudinal direction.The first gear part 145 a and the second gear part 145 b are configuredsuch that the diameter of the first gear part 145 a differs from thediameter of the second gear part 145 b. In the present embodiment, thediameter of the first gear part 145 a is configured to be smaller thanthe diameter of the second gear part 145 b.

The second relay transmission gear 146 has a first gear part 146 a thatengages the first output shaft gear 141, a second gear part 146 b thatengages the second output shaft gear 142, and a second relay shaft 146 cthat supports the first gear part 146 a and the second gear part 146 b.The second relay shaft 146 c is integrally formed with the first gearpart 146 a, engaged by spline engagement with the second gear part 146b, and doubles as a coupling member that couples the first gear part 146a and the second gear part 146 b in an interlocked manner. The secondrelay shaft 146 c is rotatably supported by the gear case 132 a and thesupporting wall part 134 in a state of extending in the vehicle bodylongitudinal direction. The first gear part 146 a and the second gearpart 146 b are configured such that the diameter of the first gear part146 a differs from the diameter of the second gear part 146 b. In thepresent embodiment, the diameter of the first gear part 146 a isconfigured to be smaller than the diameter of the second gear part 146b.

The first relay transmission gear 145 and the second relay transmissiongear 146 are coupled in an interlocked manner by a gear train 147provided spanning a rear portion of the first relay transmission gear145 and a rear portion of the second relay transmission gear 146.Specifically, as shown in FIG. 10, the gear train 147 is providedspanning a region 145 r of the first relay shaft 145 c that is locatedon the rear side with respect to the first gear part 145 a and thesecond gear part 145 b of the first relay transmission gear 145 and aregion 146 r of the second relay shaft 146 c that is located on the rearside with respect to the first gear part 146 a and the second gear part146 b of the second relay transmission gear 146. The gear train 147 canbe removed rearwardly with respect to the first relay transmission gear145 and the second relay transmission gear 146.

The gear train 147, as shown in FIG. 10, has only a first relay gear 147a that is coupled in an interlocked manner to the first relaytransmission gear 145 and a second relay gear 147 b that is coupled inan interlocked manner to the second relay transmission gear 146 in astate of engaging on the first relay gear 147 a. The first relay gear147 a is coupled in an interlocked manner to the first relay shaft 145 cby spline engagement, and is coupled in an interlocked manner to thefirst relay transmission gear 145. The first relay gear 147 a and thefirst and second gear parts 145 a and 145 b of the first relaytransmission gear 145 are supported by the same shaft, namely, the firstrelay shaft 145 c.

The second relay gear 147 b is engaged by spline engagement with thesecond relay shaft 146 c, and is coupled in an interlocked manner to thesecond relay transmission gear 146. The second relay gear 147 b and thefirst and second gear parts 146 a and 146 b of the second relaytransmission gear 146 are supported by the same shaft, namely, thesecond relay shaft 146 c.

A gear shift mechanism M that shifts the power of the input shaft 133 topower having four different rotation speeds and transmits resultantpower to the output shaft 140 is constituted by the first input shaftgear 135, the second input shaft gear 136, the input shaft sleeve 137,the first relay transmission gear 145, the gear train 147, the secondrelay transmission gear 146, the first output shaft gear 141, the secondoutput shaft gear 142 and the output shaft sleeve 143.

In the power take-off apparatus 130, in response to the first inputshaft gear 135 and the second input shaft gear 136 being alternativelycoupled in an interlocked manner to the input shaft 133 by the inputshaft sleeve 137, and the first output shaft gear 141 and the secondoutput shaft gear 142 being alternatively coupled in an interlockedmanner to the output shaft 140 by the output shaft sleeve 143, the gearshift mechanism M switches between a first transmission state, a secondtransmission state, a third transmission state and a fourth transmissionstate, and the rotation speed of the power take-off shaft 131 is changedthrough four steps.

That is, when the first input shaft gear 135 is coupled in aninterlocked manner to the input shaft 133 by the input shaft sleeve 137and the first output shaft gear 141 is coupled in an interlocked mannerto the output shaft 140 by the output shaft sleeve 143, the gear shiftmechanism M enters the first transmission state. When the gear shiftmechanism M enters the first transmission state, the power of the inputshaft 133 is transmitted to the output shaft 140 via the input shaftsleeve 137, the first input shaft gear 135, the first relay transmissiongear 145, the gear train 147, the second relay transmission gear 146,the first output shaft gear 141 and the output shaft sleeve 143, and thepower take-off shaft 131 is driven at a rotation speed that is set bythe first transmission state.

When the first input shaft gear 135 is coupled in an interlocked mannerto the input shaft 133 by the input shaft sleeve 137 and the secondoutput shaft gear 142 is coupled in an interlocked manner to the outputshaft 140 by the output shaft sleeve 143, the gear shift mechanism Menters the second transmission state. When the gear shift mechanism Menters the second transmission state, the power of the input shaft 133is transmitted to the output shaft 140 via the input shaft sleeve 137,the first input shaft gear 135, the first relay transmission gear 145,the gear train 147, the second relay transmission gear 146, the secondoutput shaft gear 142 and the output shaft sleeve 143, and the powertake-off shaft 131 is driven at a rotation speed that is set by thesecond transmission state.

When the second input shaft gear 136 is coupled in an interlocked mannerto the input shaft 133 by the input shaft sleeve 137 and the firstoutput shaft gear 141 is coupled in an interlocked manner to the outputshaft 140 by the output shaft sleeve 143, the gear shift mechanism Menters the third transmission state. When the gear shift mechanism Menters the third transmission state, the power of the input shaft 133 istransmitted to the output shaft 140 via the input shaft sleeve 137, thesecond input shaft gear 136, the first relay transmission gear 145, thegear train 147, the second relay transmission gear 146, the first outputshaft gear 141 and the output shaft sleeve 143, and the power take-offshaft 131 is driven at a rotation speed that is set by the thirdtransmission state.

When the second input shaft gear 136 is coupled in an interlocked mannerto the input shaft 133 by the input shaft sleeve 137, and when thesecond output shaft gear 142 is coupled in an interlocked manner to theoutput shaft 140 by the output shaft sleeve 143, the gear shiftmechanism M enters the fourth transmission state. When the gear shiftmechanism M enters the fourth transmission state, the power of the inputshaft 133 is transmitted to the output shaft 140 via the input shaftsleeve 137, the second input shaft gear 136, the first relaytransmission gear 145, the gear train 147, the second relay transmissiongear 146, the second output shaft gear 142 and the output shaft sleeve143, and the power take-off shaft 131 is driven at a rotation speed thatis set by the fourth transmission state.

Other Embodiments of the Second Embodiment

(1) In the embodiment described above, the gear train 147 has only thefirst relay gear 147 a and the second relay gear 147 b, but these geartrains may have three or more relay gears.

(2) In the embodiment described above, the first relay gear 147 a andthe first and second gear parts 145 a and 145 b of the first relaytransmission gear 145 are supported by the same first relay shaft 145 c,and the second relay gear 147 b and the first and second gear parts 146a and 146 b of the second relay transmission gear 146 are supported bythe same second relay shaft 146 c, but the present invention is notlimited thereto. For example, the first relay gear 147 a and the firstand second gear parts 145 a and 145 b of the first relay transmissiongear 145 may be supported by separate shafts, and the second relay gear147 b and the first and second gear parts 146 a and 146 b of the secondrelay transmission gear 146 may be supported by separate shafts. Also,the first relay gear 147 a and the first and second gear parts 145 a and145 b of the first relay transmission gear 145 may be supported by thesame first relay shaft 145 c, and the second relay gear 147 b and thefirst and second gear parts 146 a and 146 b of the second relaytransmission gear 146 may be supported by separate shafts. Also, thesecond relay gear 147 b and the first and second gear parts 146 a and146 b of the second relay transmission gear 146 may be supported by thesame second relay shaft 146 c, and the first relay gear 147 a and thefirst and second gear parts 145 a and 145 b of the first relaytransmission gear 145 may be supported by separate shafts.

(3) In the embodiment described above, the gear train 147 is providedspanning the region 145 r of a rear portion of the first relay shaft 145c and the region 146 r of a rear portion of the second relay shaft 146c, but this gear train may be provided spanning a region of the firstrelay shaft 145 c on a front side with respect to the first gear part145 a and the second gear part 145 b and a region of the second relayshaft 146 c on a front side with respect to the first gear part 146 aand the second gear part 146 b.

(4) In the embodiment described above, a configuration was adopted inwhich the first relay shaft 145 c of the first relay transmission gear145 doubles as a coupling shaft that couples the first gear part 145 aand the second gear part 145 b in an interlocked manner, and aconfiguration was adopted in which the second relay shaft 146 c of thesecond relay transmission gear 146 doubles as a coupling shaft thatcouples the first gear part 146 a and the second gear part 146 b in aninterlocked manner, but the present invention is not limited thereto. Aconfiguration may be adopted in which, in the first relay transmissiongear 145 (second relay transmission gear 146), the first gear part 145 a(146 a) and the second gear part 145 b (146 b) are provided in a stateof being integrally formed or in a state of being coupled in aninterlocked manner by a coupling member, and the first gear part 145 a(146 a) and the second gear part 145 b (146 b) are supported bydedicated shafts. In this case, the gear train 147 will not be coupledto the shafts of the first gear part 145 a (146 a) and the second gearpart 145 b (146 b), but will be coupled in an interlocked manner to themember coupling the first gear part 145 a (146 a) and the second gearpart 145 b (146 b).

What is claimed is:
 1. A work vehicle comprising: a wheel differentialmechanism having an output shaft and a differential case; an axlelocated on a vehicle body lateral outer side of the wheel differentialmechanism and interlocked with the output shaft; a planetary reductionmechanism provided between the output shaft and the axle, and configuredto downshift power of the output shaft and transmit resultant power tothe axle; a brake configured to apply friction braking power to the axlevia the output shaft, the brake having a friction plate latched to aregion of the output shaft between the differential case and theplanetary reduction mechanism; and a support member supporting theoutput shaft between the differential case and the planetary reductionmechanism, the support member being configured to engage the outputshaft relative immovably in a direction along an axis of the outputshaft.
 2. The work vehicle according to claim 1, wherein the supportmember supports a region of the output shaft between the friction plateand the planetary reduction mechanism.
 3. The work vehicle according toclaim 1, wherein the support member is a bearing that fits onto theoutput shaft.
 4. The work vehicle according to claim 3, wherein thebrake includes a friction plate receiving part supporting the frictionplate pressed in the direction along the axis of the output shaft, andthe bearing is supported by the friction plate receiving part.
 5. Apower take-off apparatus for a work vehicle, comprising: an input shaft;an output shaft to which power of the input shaft is transmitted; apower take-off shaft coupled in an interlocked manner to the outputshaft, and configured to take off the power of the output shaft andoutput resultant power to an apparatus to be driven; and a gear shiftmechanism configured to shift the power of the input shaft to powerhaving four different rotation speeds and transmit resultant power tothe output shaft, wherein the gear shift mechanism includes: a firstgear train having a first input shaft gear relatively rotatablysupported by the input shaft and a first output shaft gear relativelyrotatably supported by the output shaft, and configured to transmit thepower of the input shaft to the output shaft at a firstspeed/transmission ratio, in response to the first input shaft gearbeing coupled in an interlocked manner to the input shaft and the firstoutput shaft gear being coupled in an interlocked manner to the outputshaft; a second gear train having a second input shaft gear relativelyrotatably supported by the input shaft and a second output shaft gearrelatively rotatably supported by the output shaft, and configured totransmit the power of the input shaft to the output shaft at a secondspeed/transmission ratio different from the first speed/transmissionratio, in response to the second input shaft gear being coupled in aninterlocked manner to the input shaft and the second output shaft gearbeing coupled in an interlocked manner to the output shaft; and a relaytransmission shaft coupled in an interlocked manner to the first outputshaft gear via a first relay transmission gear mechanism having a firstrelay speed/transmission ratio, and coupled in an interlocked manner tothe second output shaft gear via a second relay transmission gearmechanism having a second relay speed/transmission ratio different fromthe first relay speed/transmission ratio, and wherein the power take-offapparatus further comprises: a first operation part configured toalternatively couple the first input shaft gear and the second inputshaft gear to the input shaft in an interlocked manner; and a secondoperation part configured to alternatively couple the first output shaftgear and the second output shaft gear to the output shaft in aninterlocked manner.
 6. The power take-off apparatus for a work vehicleaccording to claim 5, wherein the input shaft, the output shaft and therelay transmission shaft are positioned on a straight line extending ina vehicle body vertical direction, when viewed in a vehicle bodylongitudinal direction.
 7. The power take-off apparatus for a workvehicle according to claim 5, wherein the first gear train has only thefirst input shaft gear and the first output shaft gear in an engagedstate, and the second gear train has only the second input shaft gearand the second output shaft gear in an engaged state.
 8. The powertake-off apparatus for a work vehicle according to claim 5, wherein thefirst relay transmission gear mechanism is a first relay transmissiongear relatively non-rotatably supported by the relay transmission shaftin a state of engaging the first output shaft gear, and the second relaytransmission gear mechanism is a second relay transmission gearrelatively non-rotatably supported by the relay transmission shaft in astate of engaging the second output shaft gear.
 9. The power take-offapparatus for a work vehicle according to claim 5, wherein the firstoutput shaft gear and the second output shaft gear are supported by theoutput shaft via a taper roller bearing.
 10. A power take-off apparatusfor a work vehicle, comprising: an input shaft; an output shaft to whichpower of the input shaft is transmitted; a power take-off shaft coupledin an interlocked manner to the output shaft, and configured to take offthe power of the output shaft and output resultant power to an apparatusto be driven; a gear shift mechanism configured to shift the power ofthe input shaft to power having four different rotation speeds andtransmit resultant power to the output shaft, wherein the gear shiftmechanism includes: a first input shaft gear and a second input shaftgear having different diameters and relatively rotatably supported bythe input shaft in a state of being alternatively coupled in aninterlocked manner to the input shaft; a first output shaft gear and asecond output shaft gear having different diameters and relativelyrotatably supported by the output shaft in a state of beingalternatively coupled in an interlocked manner to the output shaft; afirst relay transmission gear having a first gear part that engages thefirst input shaft gear and a second gear part that engages the secondinput shaft gear; a second relay transmission gear having a first gearpart that engages the first output shaft gear and a second gear partthat engages the second output shaft gear; and a gear train configuredto couple the first relay transmission gear and the second relaytransmission gear in an interlocked manner.
 11. The power take-offapparatus for a work vehicle according to claim 10, wherein the geartrain has only a first relay gear coupled in an interlocked manner tothe first relay transmission gear, and a second relay gear coupled in aninterlocked manner to the second relay transmission gear in a state ofengaging the first relay gear.
 12. The power take-off apparatus for awork vehicle according to claim 11, wherein the first relay gear and thefirst and second gear parts of the first relay transmission gear aresupported by a same first relay shaft, and the second relay gear and thefirst and second gear parts of the second relay transmission gear aresupported by a same second relay shaft.
 13. The power take-off apparatusfor a work vehicle according to claim 12, wherein the first relay shaftand the second relay shaft extend in a vehicle body longitudinaldirection, and the gear train is provided spanning a region of the firstrelay shaft located on a rear side with respect to the first and secondgear parts of the first relay transmission gear and a region of thesecond relay shaft located on a rear side with respect to the first andsecond gear parts of the second relay transmission gear.